Evidence for the participation of a host enzyme in the activation of poly (A)-Qbeta RNA as an infectious agent.

It has been reported earlier that phage Qbeta RNA (Gilvarg, C., Bollum, F.J. and Weissmann, C. (1975) Proc. Natl. Acad. Sci. U.S. 72, 428-432) elongated at its 3' terminus with up to 100 or more AMP residues retained its full infectivity for Escherichia coli spheroplasts, and that the resulting progeny did not inherit the poly (A) appendage. We now show that while poly (A)-Qbeta RNA appears to function normally as messenger for the synthesis of virus-specific proteins it has lost its capacity to serve as template for Qbeta replicase. Template function could be restored by phosphorolysis with polynucleotide phosphorylase. Taken in conjunction, these results imply that after poly (A)-Qbeta RNA enters the spheroplast a host enzyme (perhaps polynucleotide phosphorylase) removes part or all of the adenylate residues prior to replication of the RNA.